Thanks Colin, Zenofmud and Ukmoose. after performing the procedure suggested by Mr Zenofmud the dashboard started working!
Thanks a lot guys!!!! I´m very happy!!!!
pi@raspberrypi:~/.node-red $ node-red-start
Start Node-RED
Once Node-RED has started, point a browser at http://192.168.0.84:1880
On Pi Node-RED works better with the Firefox or Chrome browser
Use node-red-stop to stop Node-RED
Use node-red-start to start Node-RED again
Use node-red-log to view the recent log output
Use sudo systemctl enable nodered.service to autostart Node-RED at every boot
Use sudo systemctl disable nodered.service to disable autostart on boot
To find more nodes and example flows - go to http://flows.nodered.org
Starting as a systemd service.
Started Node-RED graphical event wiring tool.
20 Nov 14:37:41 - [info]
Welcome to Node-RED
20 Nov 14:37:41 - [info] Node-RED version: v0.19.4
20 Nov 14:37:41 - [info] Node.js version: v8.11.1
20 Nov 14:37:41 - [info] Linux 4.14.71-v7+ arm LE
20 Nov 14:37:47 - [info] Loading palette nodes
20 Nov 14:37:56 - [info] Dashboard version 2.11.0 started at /ui
20 Nov 14:37:57 - [info] Settings file : /home/pi/.node-red/settings.js
20 Nov 14:37:57 - [info] Context store : 'default' [module=memory]
20 Nov 14:37:57 - [info] User directory : /home/pi/.node-red
20 Nov 14:37:57 - [warn] Projects disabled : editorTheme.projects.enabled=false
20 Nov 14:37:57 - [info] Flows file : /home/pi/.node-red/flows_raspberrypi.json
20 Nov 14:37:57 - [info] Server now running at http://127.0.0.1:1880/
20 Nov 14:37:57 - [warn]
Your flow credentials file is encrypted using a system-generated key.
If the system-generated key is lost for any reason, your credentials
file will not be recoverable, you will have to delete it and re-enter
your credentials.
You should set your own key using the 'credentialSecret' option in
your settings file. Node-RED will then re-encrypt your credentials
file using your chosen key the next time you deploy a change.
20 Nov 14:37:57 - [info] Starting flows
20 Nov 14:37:58 - [info] Started flows
20 Nov 14:37:58 - [info] serial port /dev/ttyUSB0 opened at 115200 baud 8N1
